In the plants for processing and/or transforming the plastic materials into granules, the granular material is typically moved from a storage container into one or more utilization machines, usually composed by injection presses or by thermoforming presses, by using a plant with a pneumatic channeling system.
The latter preferably use of the depression technique to pick up from specific containers the granular material mentioned above.
In particular, according to the prior art, the devices for pneumatic channeling comprise an emptying device of storage containers of granular material or the like equipped with a vacuum source, for example a vacuum pump that generates a low pressure which is directed towards the storage container by using a specific suction head. As a consequence, this low pressure provoques the suction of the air and, together with it, of granular material of the container.
The material is carried by the air along specific pipes towards a collection tank named receiver or feeder. On the other hand, the air carrying the granular material is directed towards the vacuum source.
The storage container holding the granular material to be carried is typically made of a nylon sack (or any other material with a polymer basis), placed inside another container, typically made by paperboard or any other equivalent material with the same rigidity. In other cases, different containers are used, for example the typology called big bag.
One of the most difficult problems to be solved in the pneumatic transportation by suction of the granular material is to carry all the material contained in the storage container without leaving leftovers.
According to the prior art this is avoided by an operator who carries moves the suction head so that it can pick up also the left granular material.
It is evident that this solution has the drawback of needing the presence of an operator that increase the production costs.
Consequently, they are known emptying devices of storage containers provided with automatic moving groups of the suction head so that this head can get up to the bottom of the sack.
This solution, even though it decreases the leftover of granular material in the sack at the end of the picking-up operation, it does not permit to reduce this leftover to the minimum or to completely eliminate it.
They are so known emptying devices having a ring holding the access opening of the sack in order to lift it during the suction of the material contained in it. In this way, the sack is totally lifted and this lifting leads to the channeling of the material towards the suction head.
However, since the majority of the sacks is thermowelded in the inferior part, their complete lifting does not provoque the deformation of the basis and, as a consequence, it does not permit to move the leftovers of granular material towards the suction head.